Most semiconductor integrated circuit manufacturing processes have some form of unit process output that can be monitored at the process step to ensure that the manufacturing tool is functioning properly. Sheet resistance is one example of a unit process output that can be monitored and measured at the process step.
However, some process outputs cannot be measured at the process step; because the complete testing structure has not been constructed. For example, in wafer level reliability (WLR) testing of certain oxides, for example gate oxides and tunnel oxides, it may take several days to complete the structure that will actually be used to test the oxide. As an illustrative example, an oxidation process may be followed sequentially by a polysilicon deposition process, a polysilicon doping process, a photolithography process, and an etching process, all of which must be performed to provide the structure necessary for WLR testing of the oxide. Due to the aforementioned four additional process steps which must be performed before the oxide can be tested, several days can elapse between the oxidation process and the electrical testing of the oxide produced by that process.
Moreover, and continuing with the aforementioned oxide example, even after electrical testing of the oxide has been performed, a test analysis engineer must then analyze and interpret the electrical test data and then determine and implement an action plan. For example, if the test analysis engineer determines from the test data that a particular tool involved in the oxidation process is not performing properly, the engineer can inform personnel in control of the wafer fabrication process that the particular tool should be removed from the manufacturing process, whereupon tool repair, tool replacement or other appropriate action can be taken.
As demonstrated above, even after the electrical testing has been completed, a significant additional amount of time can be required for the test analysis engineer to perform the test data analysis and interpretation, and then to communicate an appropriate recommendation to the wafer fabrication personnel, and then for the wafer fabrication personnel to receive the recommendation and ultimately take the necessary step(s) to remove the tool from the process flow. It is therefore not uncommon for at least an additional day to elapse between the completion of the electrical testing and the removal of a defective tool from the manufacturing process.
As demonstrated by the foregoing example, a significant amount of time (several days) can elapse before any determination that the aforementioned oxidation process is defective and should be shut down. During this entire amount of elapsed time, i.e., for several days, the oxidation process continues to operate, thereby potentially producing several days' worth of defective, useless material. This of course translates directly into a financial loss, the magnitude of which can easily reach hundreds of thousands of dollars for some processes.
It is desirable in view of the foregoing to reduce the time that elapses between the performance of a semiconductor manufacturing process step and the detection of a defect in that process step.